A power law with high energy exponential rolloff.

_{}

par1 = a |
power law photon index |

par2 = b |
e-folding energy of exponential rolloff (in keV) |

norm = |
Photons keV |

If POW_EMIN and POW_EMAX have been
defined by the **xset** command then the norm becomes the flux in units of
10^{-12} ergs cm^{-2} s^{-1} over the energy range
(POW_EMIN, POW_EMAX) keV unless POW_EMIN = POW_EMAX in which case the norm
becomes the flux density in micro-Jansky at POW_EMIN keV. In these cases it is
important that POW_EMIN and POW_EMAX lie within the energy range on which the
model is being evaluated.